1. Field of the Invention
The present invention relates to a liquid jetting apparatus forcibly discharging a liquid which has flowed back into a liquid jetting head.
2. Description of the Related Art
As an example of a conventional liquid jetting apparatus, an ink jetting apparatus such as an ink-jet printer is known. A common ink jetting apparatus includes an ink-jet head having a plurality of nozzles jetting inks and a plurality of driving parts corresponding to the nozzles, and at the time of printing, in response to the selective operation of each of the driving parts, the ink is jetted from a corresponding one of the nozzles toward a paper. Further, at the time of maintenance, after a nozzle cap is placed on a nozzle surface of the ink-jet head, a pump sucks air in the nozzle cap. Consequently, the inks with increased viscosities and bubbles in the ink-jet head are forcibly discharged into the nozzle cap.
A process of forcibly discharging the inks with increased viscosities and bubbles is generally called “purge”. In the “purge” of a type using a vacuum pump for sucking, a magnitude of a negative pressure in the nozzle cap becomes higher than a magnitude of a negative pressure in the ink-jet head, so that the inks with increased viscosities and so on in the ink-jet head are forcibly discharged as described above. However, after the vacuum pump is stopped, since the pressure in the ink-jet head is kept at the negative pressure though the negative pressure in the nozzle cap is released, there is a risk that the inks in the nozzle cap may flow back toward the inside of the nozzles. Therefore, in an ink jetting apparatus capable of color printing and thus jetting a plurality of color inks, “color mixture” in the nozzles is likely to occur because the color inks mixed in the nozzle cap may flow back toward the nozzles. When the mixed color ink is jetted at the time of the printing, printing quality is greatly impaired.
Therefore, it is a conventional practice that a forced ink jetting operation (that is, idle jetting operation) called “color mixture preventive flushing” by the driving parts is executed after the “purge”, whereby the inks which have flowed back into the nozzles are discharged from the nozzles together with the inks that they should originally jet.